Situational awareness and running shoes would be my semi-unsolicited 2-cents as well.

(the TL;DR part follows)
A relatively well-mannered person that avoids obviously dangerous scenarios and who is able to flee with appreciable speed will last a lot longer than a kid with a knife in his pocket who feels safe/complacent because he is “armed”. Even with a flashlight, kubaton, battle pen, or other such punch-load, the time and attention taken to deploy such a meager advantage could probably better be used attempting to defuse or escape the situation. This is not to discount the use of weapons when they can be obtained, but in a place where choices might be limited (like a school), one might be better off running away or using items found in the area at the time. Hence, situational awareness.

Survival is important, but as a criminal engaged in a violent confrontation involving the use of illegal weapons, survival would be your only compensation for victory. The normal life you had before said confrontation would probably be over if you were later indicted for assault with a deadly weapon or murder – probably whether you were found guilty or not.

That said, since you will be committing a crime by possessing switchblades, gravity knives, and knuckles, you might be better off just smuggling a handgun into the state and using that (hypothetically).
Either that, or become proficient in the fabrication, concealment, and use of shanks, as this is one of the few options you will have available if any fights involving concealed weapons land you in prison – where running will be less effective.

Let me clarify by saying that I do not think you are a criminal, so I would advise putting silly weapons and gadgets out of your mind. If you must carry something to feel safe, consult the law in your region and get something it allows. However, also consider the possibility that the placebo effect one might get from possessing “combat key-chains” and the like could negatively effect some of the alertness that you should be cultivating (as a “black belt”).

In addition, if it’s something you’re not familiar with using as a weapon against a motivated, resisting opponent, it’s probably not going to be particularly effective in the adrenaline rush or shock of an emergency.

Far better to try to be able to know when something’s not right and get out quick (in my opinion).

As somebody who's been on the recieving end of a tactical folder, any knife you can legally carry is useless unless you go for the throat, and a serious liability if you do. Sprint, do some cardio, and for heaven's sake, Judo.

I was going to suggest Mace but DAMN Massachusetts is a freaking nanny state! No mace either.

Looks like comfortable shoes and a cell phone are are you can really have. I'd get a bottle opener keychain that ISN'T marketed as a weapon as a last ditch tool but still you better not hurt anyone in Massachusetts.

I used to carry a neat little item we liked to call an 'ugly stick'. Basically, it is a hand held piece of wood that you should be able to grip firmly in your clenched hand with about an inch or so extra on either end and a very small nub should protrude from between your middle and ring finger.
To most, it appears to be nothing more than a whittling stick (and that is what you tell people it is) , it is perfectly legal -anywhere. Although mine did get taken from me at the front door of a club in Toronto when I forgot to leave it in the car.
The ugly stick is a nice little equalizer..if properly applied to certain points on the body, well..you get the idea. It can be a very nasty little weapon. A decent alternative to one of those key ring kubotans or whatever they are called.
I actually need to make another one, since my last one was taken from me at that club. They told me to pick it up at the end of the night when I was leaving, but of course I forgot - being drunk and all.
But, as mnay others have said- the best self defense is always being aware of your surroundings. Look like you KNOW where you are going and how to get there at all times. And don't hang around with idiots..

Last edited by OZZ; 8/16/2010 12:04pm at .

" If one wants to have a friend one must also want to wage war for him: and to wage war one must be capable of being an enemy." - Fr. Nietzsche 'On The Friend' Thus Spake Zarathustra

After having read each response, may I make a suggestion? Actually know the basic laws for weapons in your state. I had to learn that one the shock value way.

I took two years of karate In Japan, and the nunchaku was okay.... Fly back home to California, instant felony arrest potential. Fortunately for me, I was never arrested before being able to dispose of it appropriately. But, it really hit home for me how people walk into trouble not meaning to. I could have permanently lost rights and lost future employment potential right there, over nothing.

The laws were made to control the few bad apples in the bunch, but written for ease of enforcement, which means it is easy to apply to anyone, even people who are only boxing the air for exercise. In this case, the law was about possession, and not about intent.

Knowing the relevant laws of each place you are in will serve you well. Please really hear this suggestion. If you are 18 now, and have another potential 60 years to live, those future 60 will be much easier if you don't have an arrest record, especially not one involving weapons.